1. Field of the Invention
The present invention relates to a sheet processing apparatus having a conveying unit for performing a post process such as aligning or binding sheets on a processing tray and discharging an obtained sheet bundle to a paper receiving tray and a sheet processing method.
2. Description of the Related Art
In U.S. Pat. No. 5,385,340, a sheet post-processing apparatus is described. The apparatus stacks and stores a plurality of sheets with images recorded, which are sent from an image forming apparatus, on a processing tray which is a fixed loading section, staples the rear ends of the sheets, and forms a sheet bundle. Thereafter, the stopper plate strikes the sheet bundle and furthermore, the stopper plate moves and presses out the sheet bundle from the processing tray onto the storing tray. In this apparatus, the stopper plate is positioned firstly at the rear end of the processing tray and aligns the rear ends of sheets sent from the image forming apparatus. When sheets of the selection number are stacked on the processing tray, the stapling unit operates and staples the rear ends of sheets, and the stopper plate starts movement and conveys the sheet bundle.
On the other hand, in this kind of apparatus, originally, the stopper plate presses out the sheet bundle to the storing tray, that is, the sheets to be post-processed next are received by the processing tray, thus the processing efficiency can be improved conveniently. However, in the art aforementioned, before the stopper plate presses out the sheet bundle to the storing tray and then returns to the original home position, the stopper plate moves back and forth on the processing tray, so that the sheets to be post-processed next cannot be received by the processing tray and a long period of waiting time is necessary.
Therefore, the applicant develops the aforementioned art, thus the sheet bundle post-processed is sent to the middle part of the processing tray by the first arm and from the middle part, the second arm takes over conveyance of the sheet bundle and discharges it to the storing tray. The applicant contrives a constitution that the first arm is returned to the original home position while the second arm takes over and conveys the sheet bundle. Therefore, the return distance of the first arm can be shortened and the standby status of the next sheets can be set in a short time. During stacking sheets on the processing tray, the second arm may return to the initial position after passing the portion on the opposite side of the processing tray.
In this case, the processing time can be shortened more than that of the aforementioned art, though the first arm and second arm perform separate operations, so that it is necessary to individually prepare and connect drive sources and drive units, thus there is a fear that part expenses may be increased and the cost may be influenced adversely. Particularly, it is necessary to rotate the drive source of the first arm forward and backward and move the first arm back and forth along the processing tray. To shorten the return time, the speed can be controlled, though the control system will be complicated. Furthermore, the unit itself is inevitably made larger and when loading it in the housing of the apparatus, a problem arises that the mounting space is increased.